Error Message for Using --last with tkn task start -f

[danielhelfand]

Closes #553

This pull request is a proposal for dealing with when a user tries to use --last or -L with tkn task start -f. The response is an error is sent back to the user saying that --last shouldn't be used with -f.

This comment in #553 details my thoughts on why I believe this is the best approach for this issue.

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
• Regenerate the manpages and docs with make docs and make man if needed.
• Run the code checkers with make check
• Commit messages follow commit message best practices

Release Notes

Add error message for using --last with tkn task start -f

[tekton-robot]

The following is the coverage report on pkg/.
Say /test pull-tekton-cli-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/cmd/task/start.go	91.2%	91.3%	0.2

[danielhelfand]

/test pull-tekton-cli-unit-tests

[vdemeester]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vdemeester

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [vdemeester]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment